1. Field of the Invention
Embodiments of the present invention relate to a liquid crystal display device. More particularly, embodiments of the present invention relate to an electrically controlled birefringence liquid crystal display device operating at a normally black mode and having an enhanced contrast ratio.
2. Description of the Related Art
Liquid crystal display (LCD) devices refer to flat displays employing electro-optical properties of liquid crystal to display images. Conventional LCD devices may include absorptive, scattering, reflective, and polarization modulation-type LCD devices.
A conventional polarization modulation-type LCD device may be characterized as a twisted nematic (TN) LCD, i.e., a display device employing nematic type liquid crystal molecules between two substrates, and/or an electrically controlled birefringence (ECB) LCD, i.e., a display configured to convert optical retardation in order to control light transmittance. Application of voltage to the polarization modulation-type LCD may affect polarization of light passing through the liquid crystal layer, e.g., through the TN liquid crystal molecules, thereby controlling light transmittance in the LCD to form images. The images may be formed either in a normally white mode or in a normally black mode.
The normally white mode refers to a bright display, i.e., maximized light transmittance, under a low voltage application and to a dark display under a high voltage application. The normally black mode refers to a dark display, i.e., minimized light transmittance, under a low voltage application, e.g., a non-operational state, and to a bright display under a high voltage application. Even though the normally black mode may exhibit a relatively lower light transmittance as compared to the normally white mode, the normally black mode may be characterized with a low power consumption when many dark grey levels are displayed. Further, the normally black mode may exhibit a higher power efficiency than the normally white mode due to its ability to employ a standby power to display images when a power source is turned off. Accordingly, it may be advantageous to employ a polarization modulation-type LCD device operating at a normally black mode.
However, a manufacturing process of an LCD device operating at a normally black mode may be complex. In particular, the normally black mode may be realized by either a vertical alignment (VA) method, i.e., vertically aligning liquid crystal molecules with respect to the substrates at a low voltage state, or by an in-plane switching (IPS) method, i.e., horizontally aligning liquid crystal molecules with respect to the substrates, so that a light absorption axis of a polarizer may be perpendicular to an alignment direction of the liquid crystal molecules. As such, realizing a normally black mode may be difficult in LCD devices due to light dispersion through the liquid crystal molecules. Further, the light dispersion may decrease the contrast ratio of the LCD device. Accordingly, conventional LCD devices operating at a normally black mode may require a complex manufacturing process with high manufacturing costs.